Abstract

Cap43 protein has been tested for metal binding domains. The protein, specifically induced by nickel compounds in cultured human cells, had a new mono-histidinic motif consisting of 10 amino acids repeated three times in the C-terminus.
The 20-Ac-TRSRSHTSEG–TRSRSHTSEG (Thr341–Arg–Ser–Arg–Ser–His
346–Thr–Ser–Glu–Gly–Thr–Arg–Ser–Arg–Ser–His356
–Thr–Ser–Glu–Gly360
– peptide 1) and the 30–Ac-TRSRSHTSEG–TRSRSHTSEG–TRSRSHTSEG (Thr341
–Arg–Ser–Arg–Ser–His346
–Thr–Ser–Glu–Gly–Thr–Arg–Ser–Arg–Ser–His356
–Thr–Ser–Glu–Gly–Thr–Arg–Ser–Arg–Ser–His366
–Thr–Ser–Glu–Gly
370
– peptide 2) amino acids sequence has been analyzed as a site for Ni(II) binding.
A combined pH-metric and spectroscopic (UV–visible, CD, NMR) studies of Ni(II) binding to both fragments were performed. The 20-amino acid peptide can bind one and two metal ions while the 30-amino acid fragment one, two and three metal ions. At physiological pH, depending on the metal to ligand molar ratio, peptide 1 forms the Ni
2L species while peptide 2 the NiL, Ni2L and Ni3
L complexes where each metal ion is coordinated to the imidazole nitrogen atom of the histidine residue of the 10-amino acid fragment. Octahedral complexes at pH 8–9 and planar 4N complexes with (N
Im
, 3N
−
) bonding mode at pH above 9, are formed.
This work supports the existence of an interesting binding site at the COOH-terminal domain of the Cap43 protein.